1. Field of the Invention
The present invention relates to an abnormal mold detector that measures the pressure applied on an ejector pin which extrudes a molded item out of a mold tool (or die) and then detects breakage or abnormality of the mold tool.
2. Description of the Prior Art
FIGS. 9(a)-9(c) are front views illustrating a mold tool used for a conventional injection molder. Referring to FIGS. 9(a)-9(c), a movable side mold piece 100 with a core is depicted. A fixed side mold piece (not shown) confronts the movable side mold piece 100 and has a cavity. Both the side mold pieces can be opened or closed by moving the movable side mold piece 100 by means of drive means (not shown). An ejector plate 101 is on the side of the movable side mold piece 100 and moves by opening or closing the mold pieces. An ejector pin (not shown) is mounted on the ejector plate 101. The molded item formed by injecting a material between the cavity and the core is ejected out of the mold pieces by pushing the front end of the ejector pin when the mold pieces are parted from each other.
FIG. 9(a) shows the state where the ejector plate 101 is on the side of the movable side mold plate 100 in the mold parting step. In this case, the ejector pin protrudes toward the mold piece side to eject the molded item. The ejector pin 101 is at a normal protruding position. FIG. 9(b) shows that the mold pieces are in a closed state after the ejection step. In this case, the ejector plate 101 is biased to the farthest position from the mold piece by means of a spring. The ejector plate 101 is at a normal return position. The normal return position of the ejector plate 101 is detected by the operation piece 102 attached to the ejector plate 101 and the limit switch 103 attached to the base substrate of the mold piece.
As shown in FIG. 9(a), when the limit switch 103 is turned off in the ejection step (or in a non-operation state), the ejector plate 101 is in a normal state. As shown in FIG. 9(b), when the limit switch 103 is turned on in the ejection step (or in an operation state), the ejector plate 101 is in a normal state. Hence, if the limit switch 103, as shown in FIG. 9(c), is in an off state in the return step, it is judged that there is an abnormal state.
The failure in the return operation of the ejection plate 101 shown in FIG. 9(c) occurs due to various causes. For instance, the failure may occur by a residual substance of the molding substance or the mold lubricant injected into the hole for the ejector pin, a bent ejector pin, a deformed mold tool, or the like. If such a factor increases the sliding resistance against the ejector pin, the ejector pin is further bent, thus resulting in a farther increased sliding resistance. Finally, the ejector pin may be broken or scoring may occur between the ejector pin and the hole, so that the mold pieces cannot be separated from each other.
As described above, the return failure of the ejector plate 101 results from the occurrence of breakage due to scoring between the ejector pin and the hole. Conventionally, the return position is confirmed or detected after the mold tool has been broken. This requires the repair of the mold tool, repairing time and expenses. As described above, the conventional device cannot detect in advance the breakage of mold tools.
The present invention is made to solve the above-mentioned problems.
Moreover, the objective of the invention is to provide an abnormal mold detector that can previously detect the breakage of a mold tool with an ejector plate.
The objective of the present invention is achieved by an abnormal mold detector suitable for a mold tool (B), said mold tool having a plurality of molding pieces (the fixed side mold piece 12 and the movable side mold piece 13) for forming a molded item and an ejector pin (24, 61) for ejecting said molded item from the plurality of molding pieces when the plurality of molding pieces are separated from each other; said abnormal mold detector comprising pressure detection means (32, indirect pressure sensor 60) for detecting a pressure applied to the ejector pin to output a pressure detection signal; and abnormality detection means (50) for outputting an abnormal detection signal when the pressure applied to the ejector pin exceeds a reference value in a molded item ejection step; whereby a defective mold tool is detected.
According to the present invention, an abnormal mold detector suitable for a mold tool (3), the mold tool having a first mold piece (fixed side mold piece 12) with a cavity, a second mold piece (movable side mold piece 13) having a core and being relatively movable with respect to the first mold piece and an ejector pin (24, 61) for ejecting a molded item out of the first and second mold pieces by pushing it with the front end of the ejector pin when the first mold piece and the second mold piece are relatively separated from each other, the molded item being formed by filling a space between the cavity and the core with a substance, comprises pressure detection means (32, indirect pressure sensor 60) for detecting a pressure applied to the ejector pin to output a pressure detection signal; monitor timing setting means (sensors 52 and 53) for setting a monitor timing where the ejector pin ejects the molded item; processing means (51) for comparing the pressure detection signal with a predetermined reference value in the monitor timing set by the monitor timing setting means and then outputting an abnormal detection signal, in response to an indication from the processing means, when the pressure detection signal exceeds the reference value; whereby a defective mold tool is detected.
In the abnormal mold detector according to the present invention, the monitor timing setting means comprises a sensor (52, 53) mounted on the mold tool to output the timing in the molding step of the mold tool.
In the abnormal mold detector according to the present invention, the monitor timing setting means comprises a sensor (52, 53) mounted on the mold tool to output the timing in the molding step of the mold tool and a timer (timepiece 56) for starting the operation by a trigger signal from the sensor.
In the abnormal mold detector according to the present invention, the reference value is set in plural steps.
In the abnormal mold detector according to the present invention, time intervals for pressure detection of the pressure detection means (32, the indirect pressure sensor 60) are set to a value shorter than the pulse time width of the pressure detection signal applied to the ejector pin (24, 61).